1. Field of the Invention
The present invention relates to an image display device that is applicable to, for example, a projector using an ultrahigh-pressure mercury lamp as a light source. In the image display device of the present invention, substantially white main light emitted from a lamp or the like is partially replaced with auxiliary light emitted from a laser light source or the like. Illumination light is generated by strengthening the emission spectrum of the main light with the auxiliary light so that the light emitted from the light source is efficiently used and so that a bright image is displayed with high color reproducibility.
2. Description of the Related Art
In related projectors serving as image display devices, illumination light emitted from a given light source is separated into red, blue, and green wavelength regions, and is modulated by corresponding spacial light modulators such as liquid crystal panels. Subsequently, light beams emitted from the spacial light modulators are superimposed and projected onto the screen, thereby displaying a color image.
In such a projector, the light source is formed of an ultrahigh-pressure mercury lamp (hereinafter referred to as an xe2x80x9cUHPxe2x80x9d lamp), that provides a high luminous efficiency in the visible region, for efficient emission of illumination light.
FIG. 11 shows the emission spectrum of the UHP lamp. As shown in this figure, a sufficient light intensity can be ensured in the blue and green wavelength regions around 440 nm and 550 nm. However, the light intensity is insufficient in the red wavelength region above 600 nm. For this reason, in the related projectors, the light intensity in the blue and green wavelength regions is reduced in order to adjust the balance with the light intensity in the red wavelength region and to thereby ensure sufficient color reproducibility.
In such a case in which the light intensity in the blue and green wavelength regions is reduced to ensure balance with the light intensity in the red wavelength region, part of the illumination light emitted from the light source is wasted, and this makes the displayed image dark.
As a method for solving the above problem, the light source may be formed of a xenon lamp that has an emission spectrum with better balance than that of the UHP lamp. However, the luminous efficiency of the xenon lamp is lower than that of the UHP lamp. For this reason, when the xenon lamp is used as the light source in order to ensure a brightness equivalent to that in the UHP lamp, the power consumption is markedly increased.
In contrast, for example, Japanese Unexamined Patent Application Publication No. 2000-131665 discloses a method for generating illumination light using light sources that separately emit light beams in red, blue, and green wavelength regions. In this case, only elements such as semiconductor lasers and light-emitting diodes can be adopted as the separate light sources. However, high-output and highly versatile elements for emitting light in the blue and green wavelength regions are not readily available. Incidentally, high output can be achieved by using a plurality of low-output elements. In this case, however, the etendue of the light source (the product of the area and the radiation solid angle of the light source) increases. Consequently, even when a spacial light modulator having a diagonal size of approximately 1 inch is illuminated by such a light source, the illumination efficiency is saturated, and a bright image display is impossible.
The present invention has been made in view of the above problems, and an object of the invention is to provide an image display device in which a bright image can be displayed with high color reproducibility by efficiently utilizing illumination light emitted from a lamp or the like.
The present invention is applied to an image display device. In a light source, main light is partially replaced with auxiliary light in a wavelength region in which the intensity of the main light is less than that of the auxiliary light. That is, the image display device includes illumination-light combining means that generates illumination light by strengthening the wavelength region of the emission spectrum of the main light with the auxiliary light. Accordingly, the loss of main light is satisfactorily reduced, and the light intensity in the wavelength region in which the intensity of the main light is insufficient is compensated for. Further, illumination light emitted from the main light source formed of a lamp or the like is efficiently utilized, and a bright image can thereby be displayed with high color reproducibility.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.